Viewfinder Cover in in backlighting?

I have a question about the need for a viewfinder cover on our Pentax DSLRs (a K7 in my case). I was out on the hills the other evening, catching the last of the sunshine, and I ended up with a shot directly lit from the sun almost straight on from behind me. I was working with camera on tripod, and using remote control.

The problem was that my own shadow was in the frame when standing behind the camera, so I needed to move about 10 feet off to the left. I had been using mirror up with the remote control, but it was out of range at the required distance to keep my shadow out of shot. So I had to use the timer - 12 second option. I just pressed the shutter and walked away (focus was manual).

But I could see the sun shining into the viewfinder, and I remember always reading in books that this can mess up the metering, so you need to cover the viewfinder. But then I was thinking, no I metered the shot when I was at the camera and the viewfinder was in shadow. Once I press the shutter and the timer starts, the aperture & shutter settings are not going to change are they? I was working in Av and M modes. So I left it, and saw no issues with the exposures.

But the K7 was provided with a viewfinder cover, so I'm wondering in what situations or modes would it be necessary? Any experiences and further knowledge would be much appreciated.

I've certainly had light into the view finder affect metering.

I don't know if the timer locks exposure to be honest.Good Question. Easy to test I guess.

When we press the shutter release, providing the custom functions are set appropriately, then the exposure and focus will lock. Normally our eye will be at the viewfinder so no excess light can enter that way. If the 2 second or 12 second timer is used there's plenty of time to move away and get our own shadow out of frame.

Normally though I would be nearby and use my hand to shield the viewfinder - not touching, just acting as a shield. If the sunlight were shining directly into the viewfinder then although the exposure may be locked some light could spill onto the sensor. This would probably show up as red bands on film, not sure what effects on digital. The reason is that cameras are not 100% light tight. They are light tight enough for general purposes, but in an extreme situation such as sunlight streaming into the viewfinder and very long exposures, then some light could penetrate.

Thanks for those quick responses So, Smeggy, it has affected the metering. Do you remember what the effect was? John is saying that the risk is of some kind of light interference causing bands - I suppose this might be a bit like flare? I imagine the light would be reflected around the prism and could end up entering the sensor.

So it is a significant issue on Pentax DSLRs then? In my particular situation the other night, I had to be a good way away from the camera, and the shutters speeds were in the 30th - 90th sec range. Luckily I didn't see any poor effects, and the brightness of the images were as I expected. But it sounds like you are saying that the viewfinder cover should ideally be used.

Ideally used in challenging situations, having said which I have several of these and I haven't used one in over 20 years. So generally can be worked around without problems.

More susceptible on longer exposures. I often wear a woolly hat which I cover the camera with if need be

Thanks, I'll try and take the precaution especially if the exposure times are long.

The beauty in the design of the MZ series straps was the two pouches for the cover and a remote. I have MZ straps on all my cameras for that reason.

Regards - Steve

in a/v mode after you set the aperture with the viewfinder open to the light place a shade over it and the shutter time alters, quite a lot in certain cases,i always use the shield on long exposure.

Yes it affected the exposure. can't remember whether the shot was under or over exposed though. unerexposure makes sense as the etra light would fool the camera into thinkign the scene was lighter then it was

I don't remember anything other than the metering being thrown out so I doubt the light was strong enough in my case to get onto the sensor.

But it's simple to test. Just take a couple of hand held shots with the camera away from the eye and the sun shining to the VF and cover up the eyepiece on one of the shots

Shutter in the viewfinder would be nice addition to the next model.......

use manual... problem solved.

or if using auto anything.. use the viewfinder cap.

even using manual, if you set your exposure for arguements sake with 10 stop nd with no cover you will get "x" shutter speed put the cover on and the shutter speed will be longer by seconds, i have had it make a 10 second difference with 14 stops of nd filters. bright sunny day went from 15 to 25

Was that with your eye against the viewfinder when taking the manual reading?

The key part of my question really was whether the metered exposure would lock during the timer countdown in self-timer operation, or whether the ev setting could be altered during timer countdown by light entering the VF. As Smeggy has said, this can be tested for, and I'm going to try and test it - I'll reportback on that.

The same question occurred to me during while using the remote control, as I was raising the mirror with the first press, then moving away (allowing light into the VF) before pressing the remote again to fire the shutter. Obviously in this scenario the mirror is raised.